Thin film transistor substrates are generally known as display panel substrates for active matrix liquid crystal or organic EL panels and include a thin film transistor (TFT) disposed for each of a plurality of pixel electrodes arranged in a dot matrix. In particular, a display panel for color display includes RGB sub pixels put together to be one pixel, and therefore a thin film transistor substrate therefor has a thin film transistor disposed for each of the sub pixels, the number of which is three times that of the pixels.
In recent years, an amorphous silicon TFT with a good switching characteristic has been used as the thin film transistor (hereinafter referred to as “TFT”). The amorphous silicon TFT basically consists of an amorphous silicon layer as a semiconductor layer formed on a gate electrode with an insulating film (gate insulating film) therebetween, a drain electrode and a source electrode are disposed on the amorphous silicon layer, a channel region is formed between the source electrode and the drain electrode on the amorphous silicon layer, and one of the drain electrode and the source electrode is connected to a pixel electrode formed of a transparent conductive film.
The amorphous silicon TFT has a good switching characteristic but the electron mobility thereof is as low as 0.5 cm2/Vs in the channel region, and the TFT cannot provide high electron mobility required for display panels that will have even higher resolution/higher definition in the future. To address this, in a process of manufacturing a TFT substrate, laser annealing has been carried out, in which an amorphous silicon layer is irradiated with a laser light in a location to be a channel region, melted and recrystallized to form a polycrystalline silicon (polysilicon) layer with high electron mobility.
A conventional laser annealing method is known from PTL 1. According to the method, while a substrate is conveyed in one of the lengthwise and transverse arrangement directions of TFT forming regions set on the substrate, a microlens array including a plurality of lenses disposed corresponding to a plurality of TFT forming regions in a direction intersecting the substrate conveying direction is moved in the direction intersecting the substrate conveying direction, the lenses of the microlens array and the TFT forming regions on the substrate are placed at a position, so that when the TFT forming regions on the moving substrate reach immediately below corresponding lenses in the lens array, the lens array is irradiated with a laser light, and the plurality of lenses focuses and projects the laser light for annealing the amorphous silicon layer in each of the TFT forming regions.